A. Field of the Invention
The present invention relates generally to the field of display devices and more particularly to an alpha-numeric display array or character display having a predetermined pattern or matrix array of M columns by N rows of individually actuable illumination sources. The alpha-numeric display array is utilized either singly for the display or presentation of individual characters or for use in combination with other similar displays for messages, moving displays and the like.
B. Description of the Prior Art
Various alpha-numeric display arrays are available for the presentation of characters and messages. Typically the display array is formed by one or more individual display arrays each including a 5.times.7 array of individually actuable illumination sources to accurately depict character representations and messages. For example, one standard format provides for the generation of the 64 characters of the ASCII system. These display arrays are controlled by suitable character generator control circuitry to display predetermined messages by appropriately and selectively controlling the actuation of the predetermined matrix or array positions of each of the display arrays to display the appropriate character for a predetermined time duration.
One alpha-numeric display array of this general type is the "DATABLOX" display manufactured and sold by Chicago Miniature Lamp Works of the General Instrument Corporation located at 4433 North Ravenswood Ave., Chicago, Ill. 60640. This particular display generates a character approximately 4 inches in height and includes a five column by seven row array. This display array is assembled by the insertion and mounting of 35 individual, encapsulated LED sources in an appropriate array on a printed circuit card. This is accomplished by insertion of the device leads of each of the individual LED sources through alignment holes in the printed circuit card. After insertion, the leads of the LED sources are soldered. The printed circuit card includes conductive plating paths to form a control matrix for the LED sources. Next in the assembly process, an individual reflector assembly is positioned over each of the 35 mounted, LED sources. Further, an individual lens cap is attached over the top of each reflector assembly. The printed circuit card including mounted LED sources, reflector assemblies and lens caps is then inserted into a display front panel. The display front panel includes a front panel surface provided with an array of 35 spaces or holes adapted to interfit with the lens caps of each of the array positions. The front panel surface for example is fabricated from metal with the lens holes being stamped or cut therethrough. The front panel surface is finished with a generally nonreflective surface or coating. The lens caps are typically fabricated from a plastic material such as red, yellow or green plastic. Thus, the individual lens caps protrude and the array of lens caps are visible on the front panel of the display array. The PC board includes output connections for interconnection to character generator control circuitry.
While the display arrays of the prior art are generally suitable for their intended use, it would be desirable to improve operational characteristics and to improve the appearance and display quality of display arrays. Further, it would be desirable to simplify the manufacture and assembly of display arrays. For example, the appearance of the display array exhibits certain limitations from the standpoint of glare and reflective characteristics, field of vision characteristics and the general contrast of the overall display between the actuated and unactuated portions. Specifically, the lens caps of the unactuated array positions are readily visible under various viewing conditions in contrast to the background portions of the display array. The distinctiveness of the unactuated lens caps also results in a reduction in contrast with respect to the actuated array positions. In addition to the individual lens array positions standing out or being readily discernable against the contrasting background, contrast is also reduced in bright ambient light conditions due to reflections from the top surface of the unactuated lens positions.
Further, the assembly and manufacture of display arrays from individual component parts requires many individual steps of assembly and the assembly of a large number of individual parts. In addition, the assembly of the individual component parts does not optimize the desired predetermined relationship of the component parts and requires a high degree of labor skill by assembly personnel. For example, the encapsulated LED packages must be individually inserted with the leads of the LED passing through the printed circuit card and the LED source being positioned as closely as possible to the surface of the printed circuit card for proper alignment and maximum output efficiency. However, no matter how careful and skilled the assembly personnel, the consistency of such operations is not high and the positioning of each LED source is not highly accurate. Further, the LED sources mounted on the printed circuit board are not provided with a high degree of thermal insulation. Thus, thermal stressing of the LED chip bond can result in chip failure due to heat induced damage of the fine wire bonds on the LED chip during soldering operations of the printed circuit card. The manufacture and assembly of the 35 individual reflectors and lens caps and their attachment to the display array also involves a high degree of skill, increased handling costs and increased assembly labor.